SDI Convergence - Nederlandse Commissie voor Geodesie - KNAW

Spatial Data Infrastructure of Spain (Infraestructura de Datos Espaciales de España -
IDEE). The Web client application of this services catalog to be integrated within the
IDEE geoportal provides an easy and intuitive interface to browse and evaluate the features
of services accessible through this SDI. Additionally, it must be noted that this
services catalog complies with the most relevant standards and specifications defined
at international level, making a special emphasis on the compliance with the metadata
implementing rules of the INSPIRE Directive (EC, 2007), a Directive for establishing an
Infrastructure for Spatial Information in the European Community.
The rest of this article is structured as follows. Section 2 describes the state of the art in
metadata schemas for service description. Section 3 presents the design of the services
catalog, including a description of its architecture, the adoption of INSPIRE metadata
implementing rules for metadata modelling, and the automatic method proposed
to derive metadata from the capabilities information provided by OGC services. Section
4 describes the deployment of the services catalog in the Spain SDI. Finally, this article
ends with some conclusions and proposals for future work.
2. STATE OF THE ART IN APPROACHES TO SERVICE DESCRIPTION
Within the context of SDIs, the first approach for service description arose with the
definition of the first specifications for OGC services more than ten years ago. For descriptive
purposes, all OGC service specifications support a getCapabilities operation
to obtain service-level metadata (also named as capabilities) describing the content
and acceptable request parameters of an OGC service. The XML responses to getCapabilities
requests include information about service identification (general metadata for
discovery such as information as title, abstract, or keywords), service provider, and
available operations.
In 2005, ISO/TC211 defined an extension to the ISO 19115 (ISO, 2003a) geographic
metadata standard for the description of the specific features of services. This extension
has been defined within the context of ISO 19119 standard (ISO, 2005). This
standard aims at establishing the foundations of geographic information services. It
provides a taxonomy of geographic information services, and it extends the ISO 19115
comprehensive model with specific elements and data types for service descriptors.
This proposal has been also adopted by OGC in the definition of one of the profiles of
the CSW (Catalogue Services for the Web) protocol binding for catalog services specifications.
This profile, called “ISO Metadata Application Profile” (Voges and Senkler,
2007), proposes a combination of the models in ISO 19115 and ISO 19119 as the information
model followed by the metadata records to be managed through catalogs.
Recently, the European Commission started a procedure for the adoption of measures
to implement the INSPIRE directive as regards metadata (EC, 2008a). These implementing
measures define at an abstract level those descriptors that are essential for
the discovery of data and services. Besides, these measures are accompanied with
non-binding guidelines to establish the mapping between this set of abstract descriptors
and the most important metadata standards such as ISO 19115 or Dublin Core
(also adopted by ISO as ISO15836 (ISO, 2003b)). In particular, the guideline containing
the mapping to ISO 19115 (EC, 2008b) also includes the mapping to the specific
service descriptors defined in ISO 19119.
However, the above proposals seem insufficient to satisfy the current needs for building
applications following a Service Oriented Architectures (SOA) (Lieberman, 2003),
where the syntactic and semantic description of services is highly relevant. Nowadays,
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